A millimeter wave band becomes rather advanced for development of various wireless communication systems in the last decades. Advantages of such systems involve a possibility to operate in a wide bandwidth of transmitting signals to several GHz and an increasing of a bit rate to several Gbit/s. For example, the frequency range of 57-66 GHz is used in local wireless systems IEEE 802.11ad and WiGig which are license free in many counties. The frequency range of 71-76/81-86 GHz is even more popular and is usually used for radio relay point-to-point or point-to-multipoint communication systems.
The level of received signal power in millimeter wave range is less than signal power in traditional systems that use lower frequency band (assuming gains and distances the same). So, the level of received signal power for 60-90 GHz frequency band is 20 dB less than for frequency bands of 2, 4 and 5 GHz. Due to this fact antennas with high gain and narrow radiation pattern with the width of the main lobe about 1-5° is used in millimeter wave systems.
A narrow beam leads to two main disadvantages: difficulty in antenna alignment and sensitivity to twists and sways of supporting structures. Both disadvantages lead to increase of operating expenses of equipment services and personnel services at the object for additional antenna alignment. The problem may be solved by the non-limiting embodiments of the present technology of effective microwave communication apparatus with electronic beam scanning.
The interest in developing of various scanning antennas with high gain and of various types was caused by realization of mentioned requirements to antennas of millimeter wave band. There were some efforts to adapt phase arrays for operating in millimeter wave band. But it is difficult to realize array with a large number of antenna elements, thus, new technologies are required.
Aperture antennas with several feed antenna elements placed in a focal plane of a collimating device were described. A signal between this antenna elements is carried by microwave switches. If the signal is transmitted only to one of antenna elements the collimating device forms a radiation pattern with a predefined beam direction. In light of the above, switching between antenna elements provides switching between different beam directions. The main disadvantage of such method is losses associated with beam switching. The higher frequency leads to larger losses. Sometimes the result of such losses exceeds all the advantages of using antennas with the high gain.
The above problem was sold in the patent No RU2530330 which was published at Oct. 10, 2014. FIG. 1 shows the functional diagram of a radio relay communication system (100) described in patent No RU2530330. The system comprises a digital modem (10), a multi-channel radio frequency module (20) and a passive part of an antenna (30). In this embodiment of the technology the digital modem (10) is connected to a Digital-to-Analog Converter (DAC) (60) and an Analog-to-Digital Converter (ADC) (50) units and comprises a modem reception part (11) for processing a received signal and a modem transmission part (12) to form a transmitted signal and a beamforming module (40) connected to the modem reception part (11) and to the modem transmission part (12) through control channels (41). A received signal distribution block (21) and a transmitted signal distribution block (22) are connected with DAC (60) and ADC (50) units and with radio frequency units 1RF, 2RF, . . . NRF, that are included into the multi-channel radio frequency module (20). In the disclosed technology the beamforming module (40) is connected with the received signal distribution block (21) and the transmitted signal distribution block (22) through command channels and is not connected to the radio frequency units 1RF, 2RF, . . . NRF. Each radio frequency block 1RF, 2RF, . . . NRF is connected to one of the antenna elements 1AE, 2AE, . . . MAE of the passive part of the antenna (30). In this embodiment a signal that was generated in the modem transmission part (12) of the digital modem (10) is transmitted to the DAC (60) to form the signal on video frequency. This signal is transmitted on the input of the transmitted signal distribution block (22) which realizes the choice corresponding to the command signals from the beamforming module (40) of at least one of radio frequency units 1RF, 2RF, . . . NRF to form the signal on carrier frequency. The signal of carrier frequency flows to the at least one of antenna elements 1AE, 2AE, . . . MAE for transmission in directions of corresponding antenna elements. Further the received signal of carrier frequency that chosen by the received signal distribution block (21) to form the signal on video frequency from these directions flows to the at least one of the radio frequency units 1RF, 2RF, . . . NRF. The signal on the video frequency flows through the ADC (50) to the input of the modem reception part (11) for demodulation.
The beamforming module (40) according to the patent No RU2530330 is realized like a digital logic block and generates the command signals for the received signal distribution block (21) and the transmitted signal distribution block (22) which are based on the information that is received from the modem reception part (11) and the modem transmission part (12) through the control channels (41). The command signals flow to the received signal distribution block (21) and the transmitted signal distribution block (22) through the command channels (42). The received signal distribution block (21) and the transmitted signal distribution block (22) choose (switch) at least one radio frequency unit for processing the received signal and forming the transmitted signal corresponding to the command signals (for example, constant voltage signals to change the position of a switch). Among this the radio frequency units that were chosen are connected to the antenna elements and feeding of this antenna elements forms beams of radiation patterns of a scanning antenna in pre-defined directions.
Russian patent RU2530330 discloses that each of the received signal distribution block (21) and the transmitted signal distribution block (22) of this invention comprises at least one low frequency analog switch between several directions. Thus, the major mode is to choose only one radio frequency unit to transmit the signal in direction that is determined by the number of an active antenna element. In result a beam scanning is provided only by several prior known antenna directions. In other words, discrete scanning is provided without the opportunity to establish a continuous beam coverage area.
In one embodiment of the technology the received signal distribution block (21) and the transmitted signal distribution block (22) are implemented with the possibility to transfer a signal to several radio frequency blocks simultaneously. It allows to use the invention by a way of a radio relay communication system operating in a point-to-multipoint mode, but with discrete beam directions.
The station according to the patent No RU2530330 allows to use several types of scanning antennas without losses during beam switching because both distribution blocks are placed on a video frequency, so before or after the moment of mixing the signal to the high carrier frequency where such distribution may be with large insertion losses.
The disadvantage of the prototype is impossibility of a continuous beam scanning. In the prototype beam scanning may be only in discrete beam directions that is determined according to quantity and placement of feed antenna elements and according to distances between antenna elements along a focal plane of a collimating device. It is impossible to reduce these distances because of fixed dimensions of the antenna elements. In result there are intervals between beam directions. Due to these intervals minimum gain of an antenna is reduced so the quality of communication is reduced also. Elimination of such intervals in gain is a design goal and the solution will allow to improve quality of radio relay communication systems operating in the millimeter wave band.
Another disadvantage is limited power output of the station that is defined by the maximum power of each radio frequency unit. All not active radio frequency units are turned off or stay passive but it increases complexity of the design and reduces power usage effectiveness of radio relay station.
The advantage of the present invention is an continuous coverage area of the scanning antenna of the microwave communication apparatus with electronic beam scanning that is achieved without further signal losses.